Composite material; a ballistic resistant article made from same and method of making the article

ABSTRACT

A fiber reinforced resin composite for ballistic protection comprising a plurality of first and second plies wherein the first and second plies further comprise a woven fabric and a polymeric resin. The fabric has a Russell tightness factor of from 0.2 to 0.7 and a cover factor of at least 0.45, The fabric is impregnated with the resin, the resin comprising from 5 to 30 weight percent of the total weight of fabric plus resin. The fabric of each first and second ply comprises regions wherein the fabric is distorted from an orthogonal woven state by a distortion angle of least 30 degrees. The composite may further comprising a third ply having a surface area no greater than 50% of the surface area of a first and second ply. The ratio of the number of first plus second plies to the number of third plies is from 2:1 to 12:1.

BACKGROUND OF INVENTION

1. Field of the Invention

This invention pertains to a fiber reinforced resin composite havinganti-ballistic properties and armor articles made therefrom.

2. Description of Related Art

Anti-ballistic armor articles comprising high tenacity polymeric yarnshave been in use for some time. There is a continuing need to providehard body armor articles with increased resistance to bullets andfragments while at the same time reducing the total weight of theanti-ballistic article.

Current composites used for ballistic helmets and other complex curvedballistic articles are based on the assembly of layers of high strengthfabrics or non-woven packets of uni-directional fibers and resins.Composites and processes for fabrication of ballistic helmets and thelike are detailed in U.S. Pat. No. 3,582,990, U.S. Pat. No. 4,596,056,U.S. Pat. No. 4,656,674, U.S. Pat. No. 4,778,638 U.S. Pat. No.4,953,234, and U.S. Pat. No. 7,228,571. In each of these examples, thehigh strength fabric or non-woven packet is cut and darted to allow thefabric to take on the shape of the doubly curved article such as ahelmet. These cuts and darts create a discontinuity in the protectivearticle or cause wrinkling in the article if too few cuts and darts areused. The cuts, darts and wrinkles result in a decrease in thepenetrative resistance in the article. The art describes proposedshapes, patterns, pre-forming processes, off-setting approaches andstitching of the seams, as some means to minimize these defects.

A significant need exists for a ballistic helmet, or other doubly curvedarticle, with a minimum of cut and wrinkle flaws to allow a weightreduction and/or performance increase in the article.

The present invention provides for an anti-ballistic hard armorcomposite article of low areal weight and having acceptable ballisticresistance. The article can be produced without the need for folds orpleats in the fabric layers and with no or minimal cut or wrinkle flaws.The invention is particularly suitable for highly contoured articlessuch as a helmet, a knee protector, an arm protector and the like.

SUMMARY OF THE INVENTION

This invention pertains to a contoured fiber reinforced resin compositefor ballistic protection comprising a plurality of first and secondplies wherein the first and second plies further comprise (i) a wovenfabric made from a plurality of polymeric yarns having a yarn tenacityof from 15 grams per dtex to 50 grams per dtex and a modulus of from 200grams per dtex to 2200 grams per dtex, and (ii) a polymeric resin,wherein

-   -   (a) the fabric has a Russell tightness factor of from 0.2 to        0.7,    -   (b) the fabric has an areal weight of from 80 gsm to 510 gsm,    -   (c) the fabric has a cover factor of at least 0.45,    -   (d) the fabric is impregnated with the resin, the resin        comprising from 5 to 30 weight percent of the total weight of        fabric plus resin, and    -   (e) the fabric of each first and second ply comprises regions        wherein the fabric is distorted from an orthogonal woven state        by a distortion angle of least 30 degrees.

The invention is further directed to a composite comprising first,second and third plies, the third ply comprising (i) a woven fabric madefrom a plurality of polymeric yarns having a yarn tenacity of from 15grams per dtex to 50 grams per dtex and a modulus of from 200 grams perdtex to 2200 grams per dtex, and (ii) a polymeric resin, wherein,

-   -   (a) the surface area of a third ply is no greater than 50% of        the surface area of a first and second ply,    -   (b) the fabric has a Russell tightness factor of from 0.2 to        0.7,    -   (c) the fabric has an areal weight of from 80 gsm to 510 gsm,    -   (d) the fabric has a cover factor of at least 0.45,    -   (e) the fabric is impregnated with the resin, the resin        comprising from 5 to 30 weight percent of the total weight of        fabric plus resin, and    -   (f) the ratio of the number of first plus second plies to the        number of third plies in the composite is in the range of from        2:1 to 12:1.

The invention also describes a method of forming a curved fiberreinforced resin composite article comprising the above plies.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a perspective view of a helmet comprising a first ply.

FIGS. 1B and 1C show in further detail features of FIG. 1A.

FIG. 2 shows a perspective view of a helmet comprising a second ply.

FIG. 3 shows a perspective view of a helmet comprising a third ply.

FIG. 4 represents a cross shaped ply of Example 3.

FIG. 5 shows a view of slots cut into a circular ply of Example 3.

DETAILED DESCRIPTION

This invention pertains to a fiber reinforced resin composite comprisinga woven fabric and a polymeric resin. In some embodiments the compositemay comprise more than one type of woven fabric. Other embodiments maycomprise a combination of woven fabric and unidirectional non-wovenpackets.

Woven Fabric

The term “woven” is meant herein to be any fabric that can be made byweaving; that is, by interlacing or interweaving at least two yarnstypically at right angles. Generally such fabrics are made byinterlacing one set of yarns, called warp yarns, with another set ofyarns, called weft or fill yarns. The woven fabric can have essentiallyany weave, such as, plain weave, crowfoot weave, basket weave, satinweave, twill weave, unbalanced weaves, and the like. In someembodiments, a satin weave is preferred.

In some embodiments, each woven fabric layer has a basis weight of from50 to 800 g/m² (1.4 to 23.5 oz./sq.yd.). In other embodiments the basisweight of each woven layer is from 70 to 600 g/m² (2.9 to 17.6oz./sq.yd). In yet some other embodiments the basis weight of a wovenlayer is from 80 to 510 g/m² (4.0 to 14.7 oz./sq.yd).

In some embodiments, the fabric yarn count in the warp is 2 to 39 endsper centimeter (5 to 100 ends per inch) or even 3 to 24 ends percentimeter (8 to 60 ends/inch). In some other embodiments the yarn countin the warp is 4 to 18 ends per centimeter (10 to 45 ends/inch). In someembodiments, the fabric yarn count in the weft or fill is 2 to 39 endsper centimeter (5 to 100 ends per inch) or even 3 to 24 ends percentimeter (8 to 60 ends/inch). In some other embodiments the yarn countin the weft or fill is 4 to 18 ends per centimeter (10 to 45 ends/inch).

The fabric has a Russell tightness factor of from 0.2 to 0.7. In someembodiments the Russell tightness factor is from 0.3 to 0.5. The Russelltightness factor is a measure of the degree of fabric tightness that ispresent in any particular woven structure. Seyam [Textile Progress, Vol31, No. 3, 2002] provides a review of a number of dimensionless indicesthat can be used to determine the tightness or firmness of a particularfabric, including Russell's Tightness Factor. The factor is calculatedby the following formula:C _(fabric)=(n _(w) +n _(f))/(n _(wmax) +n _(fmax))where

-   -   n_(w)=warp density in the fabric (ends/cm)    -   n_(f)=fill density in the fabric (picks/cm)    -   n_(wmax)=maximum theoretical warp density    -   n_(fmax)=maximum theoretical fill density

The maximum theoretical end and pick density are calculated usingAshenhurst's Theory of ends plus intersections also detailed in theSeyam reference. The maximum theoretical end or pick density can bedetermined from the following formula;n _(max) =M/(M·d+d)where

-   -   n_(max)=theoretical maximum warp or fill density    -   M=weave factor    -   =(ends per weave repeat)/(intersections per weave repeat)    -   d=Diameter of the yarn when forced into a circular        cross-section.

For calculation of the yarn diameter of multifilament yarn, a packingfactor must be determined. For synthetic continuous filament yarns, suchas those utilized in this invention, a packing factor of 0.65 isrecommended by Seyam and should be used.

If the Russell tightness is below 0.2 the fabric becomes too looselyconnected to evenly form into the shape of a uniform ballistic articlesuch as a helmet. If the tightness factor is above 0.7 the fabricstructure will create excessive wrinkles or buckles as it is formed intohighly complex double curvature articles such as a helmet, and ballisticperformance will be reduced.

The fabric must also have a cover factor of at least 0.45. Cover factoris defined as the ratio of projected fabric surface area covered byyarns to the fabric surface area, and is given by the followingequation:CF=(C _(w) +C _(f) −C _(w) ·C _(f))Where:

-   -   C_(w)=warp cover factor=n_(w)×d    -   C_(f)=fill cover factor=n_(f)×d

If the cover factor is below 0.45 then the fabric becomes too open toeffectively stop small sized ballistic fragments at high velocities.

Yarns and Filaments

Fabrics are woven from multifilament yarns having a plurality offilaments. The yarns can be intertwined and/or twisted. For purposesherein, the term “filament” is defined as a relatively flexible,macroscopically homogeneous body having a high ratio of length to widthacross its cross-sectional area perpendicular to its length. Thefilament cross section can be any shape, but is typically circular orbean shaped. Herein, the term “fiber” is used interchangeably with theterm “filament”, and the term “end” is used interchangeably with theterm “yarn”.

The filaments can be any length. Preferably the filaments arecontinuous. Multifilament yarn spun onto a bobbin in a package containsa plurality of continuous filaments. The multifilament yarn can be cutinto staple fibers and made into a spun staple yarn suitable for use inthe present invention. The staple fiber can have a length of about 1.5to about 5 inches (about 3.8 cm to about 12.7 cm). The staple fiber canbe straight (i.e., non crimped) or crimped to have a saw tooth shapedcrimp along its length, with a crimp (or repeating bend) frequency ofabout 3.5 to about 18 crimps per inch (about 1.4 to about 7.1 crimps percm).

The yarns have a yarn tenacity of at least 7.3 grams per dtex. In someembodiments the yarns have a yarn tenacity in the range of from 10 to 65grams per dtex or even 15 to 50 grams per dtex. The yarns have a yarnmodulus of at least 100 grams per dtex. In some embodiments the yarnshave a yarn modulus in the range of from 150 to 2700 grams per dtex oreven 200 to 2200 grams per dtex. The yarns have a linear density of from50 to 4500 dtex or even from 100 to 3500 dtex. The yarns have anelongation to break of from 1 to 8 percent or even from 1 to 5 percent.

The filaments of the yarns are solid, that is, they are not hollow.

Fabric Fiber Polymer

The yarns of the present invention may be made with filaments made fromany polymer that produces a high-strength fiber, including, for example,polyamides, polyolefins, polyazoles, and mixtures of these.

When the polymer is polyamide, aramid is preferred. The term “aramid”means a polyamide wherein at least 85% of the amide (—CONH—) linkagesare attached directly to two aromatic rings. Suitable aramid fibers aredescribed in Man-Made Fibres—Science and Technology, Volume 2, Sectiontitled Fibre-Forming Aromatic Polyamides, page 297, W. Black et al.,Interscience Publishers, 1968.

A preferred aramid is a para-aramid. A preferred para-aramid ispoly(p-phenylene terephthalamide) which is called PPD-T. By PPD-T ismeant a homopolymer resulting from mole-for-mole polymerization ofp-phenylene diamine and terephthaloyl chloride and, also, copolymersresulting from incorporation of small amounts of other diamines with thep-phenylene diamine and of small amounts of other diacid chlorides withthe terephthaloyl chloride. As a general rule, other diamines and otherdiacid chlorides can be used in amounts up to as much as about 10 molepercent of the p-phenylene diamine or the terephthaloyl chloride, orperhaps slightly higher, provided only that the other diamines anddiacid chlorides have no reactive groups which interfere with thepolymerization reaction. PPD-T, also, means copolymers resulting fromincorporation of other aromatic diamines and other aromatic diacidchlorides such as, for example, 2,6-naphthaloyl chloride or chloro- ordichloroterephthaloyl chloride or 3,4′-diaminodiphenylether.

Additives can be used with the aramid and it has been found that up toas much as 10 percent or more, by weight, of other polymeric materialcan be blended with the aramid. Copolymers can be used having as much as10 percent or more of other diamine substituted for the diamine of thearamid or as much as 10 percent or more of other diacid chloridesubstituted for the diacid chloride or the aramid.

Another suitable fiber is one based on aromatic copolyamide prepared byreaction of terephthaloyl chloride (TPA) with a 50/50 mole ratio ofp-phenylene diamine (PPD) and 3,4′-diaminodiphenyl ether (DPE). Yetanother suitable fiber is that formed by polycondensation reaction oftwo diamines, p-phenylene diamine and 5-amino-2-(p-aminophenyl)benzimidazole with terephthalic acid or anhydrides or acid chloridederivatives of these monomers.

When the polymer is polyolefin, polyethylene or polypropylene ispreferred. The term “polyethylene” means a predominantly linearpolyethylene material of preferably more than one million molecularweight that may contain minor amounts of chain branching or comonomersnot exceeding 5 modifying units per 100 main chain carbon atoms, andthat may also contain and mixed therewith not more than about 50 weightpercent of one or more polymeric additives such as alkene-1-polymers, inparticular low density polyethylene, propylene, and the like, or lowmolecular weight additives such as anti-oxidants, lubricants,ultra-violet screening agents, colorants and the like which are commonlyincorporated. Such is commonly known as extended chain polyethylene(ECPE) or ultra high molecular weight polyethylene (UHMWPE

In some preferred embodiments polyazoles are polyarenazoles such aspolybenzazoles and polypyridazoles. Suitable polyazoles includehomopolymers and, also, copolymers. Additives can be used with thepolyazoles and up to as much as 10 percent, by weight, of otherpolymeric material can be blended with the polyazoles. Also copolymerscan be used having as much as 10 percent or more of other monomersubstituted for a monomer of the polyazoles. Suitable polyazolehomopolymers and copolymers can be made by known procedures.

Preferred polybenzazoles are polybenzimidazoles, polybenzothiazoles, andpolybenzoxazoles and more preferably such polymers that can form fibershaving yarn tenacities of 30 gpd or greater. If the polybenzazole is apolybenzothioazole, preferably it is poly(p-phenylene benzobisthiazole).If the polybenzazole is a polybenzoxazole, preferably it ispoly(p-phenylene benzobisoxazole) and more preferablypoly(p-phenylene-2,6-benzobisoxazole) called PBO.

Preferred polypyridazoles are polypyridimidazoles, polypyridothiazoles,and polypyridoxazoles and more preferably such polymers that can formfibers having yarn tenacities of 30 gpd or greater. In some embodiments,the preferred polypyridazole is a polypyridobisazole. A preferredpoly(pyridobisozazole) ispoly(1,4-(2,5-dihydroxy)phenylene-2,6-pyrido[2,3-d:5,6-d′]bisimidazolewhich is called PIPD. Suitable polypyridazoles, includingpolypyridobisazoles, can be made by known procedures.

Polymeric Resin

By “polymeric resin” is meant an essentially homogeneous resin orpolymeric material in which the yarn is embedded. The polymeric resinmay be thermoset or thermoplastic or a mixture of the two. Suitablethermoset resins include phenolic, epoxy, polyester, vinyl ester and thelike. Suitable thermoplastic resins include a blend of elastomeric blockcopolymers, polyvinyl butylral polyethylene copolymers, polyimides,polyurethanes, polyesters and the like. In some embodiments, thepolyethylene copolymers comprise from 50 to 75 weight percent and theelastomeric block copolymers comprise from 25 to 50 weight percent ofthe resin. For example ethylene copolymers with acid monomers can beused, or alternatively any polyester of polyamide may be used. Ethyleneacrylic acid copolymer is one suitable material. One skilled in the artwill be able with minimal experimentation to specify a suitable polymer.

The ethylene copolymers that may be utilized in the present inventioncan be neutralized with an ion selected form the group consisting ofsodium, potassium, lithium, silver, mercury, copper and the like andmixtures thereof. Useful divalent metallic ions include, but are notlimited to, ions of beryllium, magnesium, calcium, strontium, barium,copper, cadmium, mercury, tin, lead, iron, cobalt, nickel, zinc and thelike and mixtures therefrom. Useful trivalent metallic ions include, butare not limited to, ions of aluminum, scandium, iron, yttrium and thelike and mixtures therefrom. Useful multivalent metallic ions include,but are not limited to, ions of titanium, zirconium, hafnium, vanadium,tantalum, tungsten, chromium, cerium, iron and the like and mixturestherefrom. It is noted that when the metallic ion is multivalent,complexing agents, such as stearate, oleate, salicylate, and phenolateradicals may be included, as disclosed within U.S. Pat. No. 3,404,134.The metallic ions used herein are preferably monovalent or divalentmetallic ions. More preferably, the metallic ions used herein areselected from the group consisting of ions of sodium, lithium,magnesium, zinc and mixtures therefrom. Yet more preferably, themetallic ions used herein are selected from the group consisting of ionsof sodium, zinc and mixtures therefrom. The parent acid copolymers ofthe invention may be neutralized as disclosed in U.S. Pat. No.3,404,134.

By “degree of neutralization” is meant the mole percentage of acidgroups on the ethylene copolymer that have a counterion. The ethyleneacid copolymer utilized in the present invention is neutralized to alevel of about 70% to slightly greater than 100% with one or more metalions selected from the group consisting of potassium, sodium, lithium,magnesium, zinc, and mixtures of two or more thereof, based on the totalcarboxylic acid content of the acid copolymer.

A polymer or copolymer may also be applied to the fabric surface in theform of a dispersion, or a solution. The polymer or copolymer may alsobe plasticized. Any suitable plasticizer may be selected by one skilledin the art, for example the plasticizer is selected from the groupconsisting of fatty acids or fatty alcohols. A polymer or co-polymer mayalso be applied to the fabric in the form of a film or dry powder.Several methods may be selected by one skilled in the art to laminatethe polymer to the fabric substrate.

The amount of resin in the composite is from 5 to 30 weight percent ofthe composite based on the total weight of resin plus fabric. In someembodiments, the resin content is from 5 to 20 weight percent. In otherembodiments the resin content is from 5 to 15 weight percent. In yetanother embodiment, the resin content is from 8 to 12 weight percent.The resin may be coated onto the surface of the fabric or impregnatedbetween the yarn filaments by well known prepregging methods such asthose described in section 2.9 of “Manufacturing Processes for AdvancedComposites” by F. C. Campbell, Elsevier, 2004 or may be film or powderlaminated to the fabric.

Preform Manufacture

For handling and process efficiency purposes, a fiber reinforced resincomposite article may be assembled from a preform or a plurality ofpreforms. A preform is a formed but not fully consolidated resin coatedor impregnated fabric (prepreg) which has the contour of the finishedproduct. There may be a plurality of fabric layers in a preform.

Prepreg ply shapes are cut from prepreg roll stock using a knife andtemplate, a cutting die or some other means. One layer of cut prepregstock is called a ply. The number of shapes to be cut and the dimensionsof each shape will depend on the final design of and the materials to beused in the final article. In some embodiments, there is more than oneply shape in a preform assembly.

Cut plies are stacked in the desired sequence on a preforming tool,which may be flat or contoured and made of materials such as wood,metal, plastic, fiber-reinforced plastic or ceramic. In some instances,the layers comprising the preform are bonded under temperature andpressure. One convenient processes for achieving pre-consolidation isvacuum forming or matched mold shaping. These processes are well knownin the art. The amount of heat and pressure to bond the ply stack shouldbe sufficient to allow the particular resin to reach a melt stage whichpermits the polymer to be infused into and through the fabric thusadhering multiple plies together and providing a cohesive and semi-rigidpreform. By semi-rigid we mean that the preform is both noticeablystiffer than the prepreg and sufficiently stiff to prevent individualfabric layers from buckling and causing wrinkles during finalconsolidating in the molding tool. A single preforming step issufficient to provide the desired compaction and inter-ply coherence tothe preform.

In some instances, bonding of the layers comprising the preform isachieved by saturation with a liquid resin in a process commonly know aswet lay-up. These processes are well know in the art. The wet resinsoaked layers are layed on the preforming tool to create the desiredcontoured shape, and solvents are removed and/or the resin level of cureis advanced to create the rigid preform.

Article Manufacture

A plurality of individual plies or preforms are stacked in a desiredsequence on a molding tool having the dimensions of the finishedarticle. The tool is contoured and made of materials such as metal,plastic, fiber-reinforced plastic or ceramic. The desired number ofpreforms in the final assembly will vary according to the laminatedesign and the number of plies in each preform. The number of plies in alaminate varies from 2 to 500, or from 20 to 150 or even from 30 to 120.In a preferred embodiment, there are from 10 to 70 plies in the finalassembly. Final consolidation is carried out under temperature andpressure. The temperature can be from 115° C. to 230° C., or from 120°C. to 170° C. or even from 140° C. to 160° C. The desired consolidationpressure is achieved by applying a force of from 34 to 800 tonnes orfrom 200 to 600 tonnes or even from 400 to 650 tonnes. Once attemperature, the temperature is maintained for a specified number ofminutes before cooling is initiated. The temperature hold time can befrom 5 min to 60 min, or from 5 min to 30 min or even from 7 min to 22min. The molding of the composite laminate may be carried out in aplaten press, an autoclave, a matched mold or under vacuum in an oven,such techniques being well known to those skilled in the art. For athermoplastic polymeric resin, the amount of heat required should besufficient to allow the particular thermoplastic to reach a melt stage.The applied pressure should be sufficient to cause good compaction ofthe plies such that there are minimal voids in the finished laminate.Voids may be detected by methods such as ultrasonic scanning or x-rays.Preferably, the finished laminate is removed from the mold after it hascooled to room temperature. This allows the resin to fully solidifybefore removal from the mold. After removal of the cured laminate fromthe mold, the laminate is trimmed and sent for finishing operations suchas installation of fittings and painting.

In one embodiment, the fiber reinforced resin composite article isformed from first and second plies. FIG. 1A shows generally at 10 thecontoured shape of a helmet comprising a first ply. The warp and fill(weft) yarns are shown respectively at 11 and 12. Over the majority ofthe surface area of the first ply, the warp and fill yarns areorthogonal or essentially orthogonal to each other. By “‘essentially”orthogonal is meant that the warp and fill yarns are within a fewdegrees of being orthogonal to each other, for example within five orten degrees. An example of an orthogonal yarn intersection is shown at13 in FIG. 1B. Extending or trellising the corners or edges of a plyproduces a ply having regions where the warp and fill yarns becomedistorted from an orthogonal intersection as in the original wovenstate. This angle of yarn distortion is referred hereto as a distortionangle and is shown as Ψ at 14 in FIG. 1C. It is preferable that thedistortion angle is at least 30 degrees or even 40 degrees. A phantomcenter reference line for the first ply is shown at 15. It is notunusual for significant distortion and folding to occur at and/or aroundthe outer edges of the finished article, resulting from manufacturingimperfections. For this reason, when determining the distortion anglepresent in any article, the regions within 25.4 mm (1 inch) of the edgesshould be excluded.

FIG. 2 shows generally at 20 a second ply having warp yarns 21 and fillyarns 22. The majority of the warp and fill yarns are orientedorthogonally or essentially orthogonally to each other but, as describedfor FIG. 1, trellising the fabric of a second ply produces regions inthe ply wherein the fabric is distorted from an orthogonal woven stateby a distortion angle of least 30 degrees. A phantom center referenceline for the second ply is shown at 23.

During assembly of the composite article, the second ply is offset at anangle, alpha, of from 20 to 70 degrees with respect to the first ply.This offset angle is shown at 24 in FIG. 2 with respect to centrereference lines 15 for the first ply and 23 for the second ply.

In one embodiment, the first and second plies are stacked in analternating sequence and are oriented at from 20 to 70 degrees withrespect to each other. The first and second plies have a shape profilesimilar to the final shape profile of the article being formed.

In another embodiment, the fiber reinforced resin composite articlecomprises a third ply which is shown at 33 in FIG. 3. Also shown in thisfigure are the principal warp 11 and fill 12 yarn directions of a firstply. A requirement of the third play is that it has a surface area nogreater than 50% of the surface area of a first or second ply, If thesurface area of the third ply is greater than 50% uniformity in materialdistribution will not be maintained. During assembly of the first,second and third plies, the number of third plies is such that the ratioof the number of first plus second plies to the number of third plies inthe composite is in the range of from 2:1 to 12:1 or 3:1 to 12:1 or even4:1 to 12:1, The third plies are stacked periodically throughout theassembly, for example as every sixth ply. The orientation of the yarnsof the third ply is not critical. The prime function of the third ply isto maintain uniformity in the distribution of material throughout thearticle. The shape of the third play may be any convenient shape such ascircular, oval, square, rectangular, diamond, pentagonal, hexagonal oroctagonal.

A contoured fiber reinforced resin composite article having a uniformdistribution of material can be produced from first, second and thirdplies as described above without the need for cuts, darts, pleats orfolds in any of the plies.

An antiballistic article may also be produced as a hybrid constructioncomprising composites as described above plus fabrics of anotherconstruction. One example of another construction is a nonwoven fabriccomprising polyolefin yarns oriented in a unidirectional arrangement.These nonwoven materials may be obtained from DSM Dyneema or Honeywell.In a preferred embodiment of a hybrid construction, the layers ofpolyolefin yarns are in a strike facing direction and the layers ofwoven fabrics in a body facing direction.

Test Methods

Ballistic Penetration Performance:

Ballistic tests of the composite laminate were conducted in accordancewith standard procedures MIL STD-662F (V50 Ballistic Test for Armor, 18Dec. 1997) and NIJ STD 0106.01 (Ballistic Helmets). Tests were conductedusing 16 grain fragment simulating projectiles (FSPs) against thecomposite laminate targets. The projectiles were compliant with MIL DTL46593B. One article was tested for each examples with 10 shots, at zerodegree obliquity, fired at each target. The reported V50 values areaverage values for the number of shots fired for each example. V50 is astatistical measure that identifies the average velocity at which abullet or a fragment penetrates the armor equipment in 50% of the shots,versus non penetration of the other 50%. The parameter measured is V50at zero degrees where the degree angle refers to the obliquity of theprojectile to the target.

EXAMPLES Materials

A 4-harness satin weave Kevlar® fabric was acquired from JPS Composites,Anderson, S.C. The fabric had an areal weight of 146.4 gsm, a yarn countof 7.87 ends per cm (20 ends per inch) in the warp, a yarn count of 7.87ends per cm (20 ends per inch) in the weft, a cover factor of 0.48 and aRussell tightness factor of 0.35. The fabric was woven from Kevlar® 129,840 denier para-aramid yarn available from E. I. DuPont de Nemours andCompany, Wilmington, Del. The yarn had a nominal yarn tenacity of 29grams per dtex and a yarn modulus of 820 grams per dtex

A plain weave Kevlar® fabric was acquired from JPS Composites, Anderson,S.C. The fabric had an areal weight of 152.1 gsm, a yarn count of 7.87ends per cm (20 ends per inch) in the warp, a yarn count of 7.87 endsper cm (20 ends per inch) in the weft, a cover factor of 0.48 and aRussell tightness factor of 0.56. The fabric was woven from Kevlar® 129,840 denier para-aramid yarn available from E. I. DuPont de Nemours andCompany, Wilmington, Del. The yarn had a nominal yarn tenacity of 29grams per dtex and a yarn modulus of 820 grams per dtex

Dyneema® HB 26 is a roll product consisting of four crossed plies ofunidirectionally oriented polyethylene yarns embedded in resin. Thisnonwoven material was obtained from DSM Dyneema, Stanley, N.C. Thisfour-ply sheet had an areal weight of 260 gsm, (0.053 psf). The type offiber used in this material is reported in the literature to have anominal tenacity of about 44 grams per dtex and a modulus of about 1400grams per dtex.

Example 1

The 4 harness satin weave fabric described above was impregnated with athermoplastic resin dispersion, Michem® Prime 2960, to make a suitablewet prepreg for manufacture of a helmet shaped composite. The resin isavailable from Michelman Inc., Cincinnati, Ohio. The dry resin contentof the prepreg was 8 percent by weight of the fabric plus the dry resin.The resin is an ethylene/acrylic acid copolymer. Plies for creating ahelmet shaped article were made by cutting either 432 mm×432 mm squaresor 230 mm diameter circles.

A first fabric square ply was draped over a male mold plug that modeledthe shape of a medium sized Personnel Armor System for Ground Troops(PASGT) helmet. Each of the 4 corners of the first ply were tensioned soas to cause the fabric to distort and conform to the shape of the helmetmold as it was draped in place. A second fabric ply was then placed ontop of the first fabric ply. This second ply was also conformed to theshape of the mold by distorting the fabric plies through tensioning ofthe corners. The orientation of the second ply was rotated by 45 degreeswith respect to the orientation of the first ply. A total of 46 squareplies were positioned in a similar alternating manner between the twoorientations of first and second plies to create the shaped helmetpreform. In addition to the distorted square plies, a total of ninecircular crown plies, third plies, 230 mm in diameter, were also added,one crown ply for each five of the square plies. The circular crownplies were centered on the top of the article. Each crown ply had andarea of approximately 410 square centimeters. These plies coveredapproximately 33% of the molded PASGT helmet shape or approximately 40%of the surface area of the first and second plies.

The assembly of 55 plies was removed from the mold plug and was placedin a vacuum oven, heated to 110 degrees C. and dried for 3 hours toremove the water from the polymer coating. The dried assembly of polymercoated fabrics was placed in a matched die PASGT helmet compression moldwith a gap of 6.86 mm and pressed at a temperature of 141 degrees C. andwith 455 tonnes force. The molded was bumped open once during themolding process to release any volatiles and then held under thoseconditions for 15 minutes. While still under pressure, the compressedassembly was rapidly cooled to 38 degrees C. to complete consolidationof the structure. The shell had a molded weight of 1.04 kg, with anaverage thickness of 7.19 mm. This weight translates to a PASGT helmetweight of 0.95 kg.

The outer plies of the formed helmet were examined and a maximumdistortion angle of 55 degrees was noted in the regions of the helmetthat had been distorted to create the seamless contoured ply shape. Theregions within 25.4 mm of the trimmed helmet edge were ignored for thismeasurement to exclude any edge effects in the measurement. The helmetwas assembled without cuts, darts, pleats or folds in the first, secondand third plies.

The molded helmet was tested to determine its ballistic resistanceagainst a 16 grain Right Circular Cylinder (RCC) Fragment SimulatedProjectile (FSP). The lightweight helmet had a V₅₀ value of 831 m/s thatsurpassed by 91 m/s the performance standard published by MSA for ACHTC2000 series helmets

Example 2

The plain weave fabric described above was impregnated with athermoplastic resin dispersion, Michem® Prime 2960, to make a suitablewet prepreg. The dry resin content of the prepreg was 8.5 percent byweight of the fabric plus the dry resin. Plies for creating a helmetshaped article were made by cutting either 432 mm×432 mm squares or 230mm diameter circles.

A medium sized PASGT helmet preform was created as described in Example1, by wet lay-up of the square and circular ply shapes. A total of 55plies were again used to create the helmet preform. The ply sequencingand orientation of the first, second and third plies was as inExample 1. The preform was similarly dried, and pressed as in Example 1to create a medium PASGT shaped helmet shell. A finished helmet was cutto the contours of a typical Advanced Combat Helmet. The final helmethad a trimmed weight of 1.06 kg, with an average thickness of 7.06 mm.The outer plies of the formed helmet were examined and a maximumdistortion angle of 40 degrees was noted in the regions of the helmetthat had been distorted to create the seamless contoured ply shape. Theregions within 25.4 mm of the trimmed helmet edge were ignored for thismeasurement to exlude any edge effects in the measurement. The helmetwas assembled without cuts, darts, pleats or folds in the first, secondand third plies.

The molded helmet was tested to determine its ballistic resistanceagainst a 16 grain Right Circular Cylinder Fragment SimulatedProjectile. The lightweight helmet had a V₅₀ value of 832 m/s thatsurpassed by 92 m/s the performance standard given by MSA for ACH TC2000series helmets.

Example 3

Eight sheets of Dyeema® HB-26 were cut into circular plies having adiameter of 483 mm. Four slots each having a length of 165 mm were cutinto each circular ply as shown at 50 in FIG. 5. A further eight sheetswere cut in the shape of a cross. Plies cut in the shape of a cross allhad a length of 483 mm and a width of 108 mm as shown as L and Wrespectively in FIG. 4. The sixteen plies (8 circles and 8 crosses) werelightly tacked into a net helmet shape with an ultrasonic welding tooland stacked in an alternating fashion. The assembled stack was placedinto a matched die PASGT helmet compression mold with a gap of 8.13 mmwhich was preheated to 129 degrees C. and the mold closed for 15seconds, just long enough to make a partially consolidated firstsub-assembly which was then immediately removed from the mold.

The 4 harness satin weave aramid fabric previously described wasimpregnated with Michem® Prime 2960 resin to make a wet prepreg. The dryresin content of the prepreg was 8 weight percent based on the totalweight of fabric plus resin. The prepreg was cut into either 432 mm×432mm squares or 230 mm diameter circles. There were 22 square and 4circular plies that were assembled over a male mold plug in a similarmanner as described in Example 1 to form a second sub-assemblycomprising first, second and third plies. The circular crown plies werecentered on the top of the second sub-assembly. This second sub-assemblywas then removed from the mold plug and placed in a vacuum oven, heatedto 110 degrees C. and dried for 3 hours to remove the water from thepolymer coating. The second sub-assembly was placed into a matched diePASGT helmet compression mold with a gap of 8.13 mm which was preheatedto 129 degrees C. and the mold closed for 15 seconds, just long enoughto make a partially consolidated second sub-assembly which was thenimmediately removed from the mold

A final helmet assembly was made by inserting the second sub-assemblyinside the first sub-assembly and placing the combined assembly into amatched die PASGT helmet compression mold with a gap of 8.13 mm. Themold was preheated to a temperature of 129 degrees C. and held for 20minutes to consolidate the two sub-assemblies into a final assembly.While still under pressure, the compressed assembly was rapidly cooledto 38 degrees C. and this temperature maintained for 40 minutes tocomplete consolidation of the structure. The resulting helmet shell wascut to the contours of a typical Advanced Combat Helmet. The finalhelmet shell had a molded weight of 0.85 kg. Fifty percent of thisweight was comprised of Dyneema®HB 26 and fifty percent of this weightwas comprised of the resin impregnated aramid fabric. The averagethickness of the shell was 7.95 mm. The inner plies of the formed helmetshell were examined and a maximum distortion angle of 40 degrees wasnoted in the regions of the helmet that had been distorted to create theseamless contoured ply shapes. The regions within 25.4 mm of the trimmedhelmet edge were ignored for this measurement to ignore any edge effectsin the measurement. The helmet was assembled without cuts, darts, pleatsor folds in the woven fabrics of the second sub-assembly.

The molded helmet shell was tested to determine its ballistic resistanceagainst a 16 grain Right Circular Cylinder Fragment SimulatedProjectile. The layers of polyethylene formed the outer strike facingsection of the final assembly and the layers of aramid fabric formed theinner back facing section. The lightweight helmet had a V₅₀ value of 767m/s that surpassed by 53 m/s the performance standard given by MSA forACH TC2000 series helmets.

The ballistic results for these examples are summarized in Table 1.

TABLE 1 Shell Weight V50 Example Helmet Description (kg) (m/s) ControlACH TC2000 Series Datasheet 1.10 739 Value 1 Aramid Satin Weave Fabric0.95* 831 2 Aramid Plain Weave Fabric 1.05 832 3 Hybrid of Polyethyleneand Aramid 0.85 767 *indicates an ACH equivalent weight.

The results show that a helmet construction comprising woven fabricshaving a Russell tightness factor of from 0.2 to 0.7 and a cover factorof at least 0.45 meet the specified anti-ballistic performancestandards. Since the helmets are made without cuts, darts, pleats orfolds in the plies there is a reduction in the number of potential weakzones that could adversely impact performance in the field.

What is claimed is:
 1. A method of forming a curved fiber reinforcedresin composite article comprising the steps of (i) providing a roll ofresin impregnated fabric composite comprising a woven fabric made from aplurality of polymeric yarns having a yarn tenacity of from 15 grams perdtex to 50 grams per dtex and a modulus of from 200 grams per dtex to2200 grams per dtex, and a polymeric resin, wherein (a) the fabric has aRussell tightness factor of from 0.2 to 0.7, (b) the fabric has an arealweight of from 80 gsm to 510 gsm, (c) the fabric has a cover factor ofat least 0.5, and, (d) the fabric is impregnated with the polymericresin, the resin comprising from 5 to 30 weight percent of the of thetotal weight of fabric plus resin, (ii) cutting a plurality of pliesfrom the fabric composite roll to provide first and second plies suchthat the plies have a shape profile similar to the final shape profileof the article being formed, (iii) cutting a plurality of plies from thefabric composite roll to provide third plies such that the surface areaof a third ply is no greater than 50% of the surface area of the firstor second plies, (iv) extending or trellising the corners or edges ofthe first and second plies over a contoured tool to cause regions in theweave of the ply to distort by a distortion angle of at least 30degrees, (v) assembling, in the desired order, a plurality of first,second and third plies into a contoured shaped preform such that theratio of the number of first plus second plies to the number of thirdplies is in the range of from 2:1 to 12:1 and the orientation of asecond ply is offset at an angle of from 20 to 70 degrees with respectto the orientation of a first ply, (vi) assembling a plurality ofcontoured preforms in a desired sequence on a molding tool, and (vii)consolidating the assembly of preforms of step (vi) at a temperature offrom 115° C. to 230° C. and an applied force of from 34 to 800 tonnesfor between 5 to 60 minutes to form a cured hard armor compositearticle.
 2. The method of claim 1 wherein the polymer of the yarns ofthe first, second and third plies is para-aramid, polyazole or mixturesthereof.
 3. The method of claim 1 wherein the polymer of the yarns ofthe first, second and third plies is polyethylene.
 4. The method ofclaim 1 wherein the fabric of each first and second ply comprisesregions wherein the fabric is distorted from an orthogonal woven stateby a distortion angle of least 40 degrees.